The present invention relates to an image forming apparatus that receives waste toner in a waste toner container and to a method of controlling the image forming apparatus.
In image forming apparatus, the waste toner that has not been transferred onto paper and is remaining on a photoreceptor and the like is received in a waste toner container. Because the capacity of the waste toner container is limited, it is necessary for a waste toner container to be replaced with another empty one before it becomes full. Therefore, fullness of the waste toner in the waste toner container is detected by some means.
In the Japanese Patent Unexamined Publication No. 2003-271023 bulletin, it is described that using the number of pixels of image data counted by a pixel counter an integration of the number of the pixels is started when a waste toner reception quantity sensor detects that the quantity of received waste toner has reached a predetermined amount (near end), and that the quantity of received waste toner is judged to have become full (full end) when the integrated value reaches a predetermined value.
The above described conventional method, in which the full end is determined by the quantity of the waste toner that is not directly detected but is estimated from the number of the pixels, is therefore not necessarily correct. In case of a type of image forming apparatus adapted for color images, in particular, where waste toners are conveyed per color and then received collectively in a waste toner container, when the number of total pixels of image data is used as a parameter as described in the patent literature above, it cannot precisely reflect the image data since it is not the numbers of pixels counted per color.
That is to say, as shown in FIG. 6A, uneven frequencies in use of respective toners that tend toward one color is subject to the risk of causing the waste toner to overflow exceeding a fullness position of the waste toner container. Besides, as shown in FIG. 6B, relatively even frequencies in use of respective toners is even subject to the risk of a state actually with room and not yet in full-state being misjudged to be in full-state; and this results in an increased number of times of replacement of the waste toner container, adding to the troublesome task for a user.
The present invention was made in view of the above described problem, and is directed to providing a means to determine as precisely as possible fullness of a waste toner received to a waste toner container in an image forming apparatus adapted for color images.